Various types of stationary equipment are now commonly used to provide aerobic exercise for persons who wish to keep physically fit, and also for therapy and rehabilitation purposes for patients who have suffered an illness or injury. Common forms of stationary exercise equipment for these purposes include exercise rowing machines, stair climbing machines, skiing machines, treadmills and cycles. Of these various types of exercise equipment, exercise cycles have an advantage in that they do not place high stress on the knees, ankles or backs, which could result from jogging or rowing.
In basic form, conventional stationary exercise cycles are constructed with a frame, together with a seat and handlebars mounted on the frame in the same positions relative to each other as on a typical bicycle. Pedals and associated cranks are used to drive a drum, wheel or flywheel using various types of drive trains, for instance, sprockets and a drive chain, pulleys and a drive belt or gears and a drive shaft. A resistance load is applied to the wheel, drum or flywheel by various techniques. Perhaps the most common technique is through the use of a band brake that extends around the periphery of the drum or flywheel. Examples of such exercise cycles are disclosed by U.S. Pat. Nos. 2,510,973; 3,833,216; 3,967,503; 3,995,491; 4,419,890; 4,533,136 and 4,592,544 and by British Pat. No. 1,464,540.
To be effective, aerobic exercising, including cycling, must place an increased load on the cardiovascular, respiratory and metabolic systems of the body, with the proper level of such loads dependent upon various factors such as the physical condition, health, size and age of the individual. Thus, it is desirable that exercise equipment, including stationary exercise cycles, be capable of measuring the work being expended by the individual to ensure that a proper workout level is being achieved and also to permit the workout level to be precisely repeatable.
In exercise cycles utilizing band brakes, a desired workout level is typically attained by varying the tension on the band brake, usually by imparting a tensile load on one end of the band brake. The tension on the band brake is measured using various techniques to quantify the energy being expended by the rider. For instance, in the above-mentioned '540 British patent, the tension on the band brake is applied by and measured with a spring device resembling a fish scale having a pointer directed at a series of graduations formed on the scale. In the '973 U.S. patent, the tension on the band brake is measured with a spiral spring having an associated pointer indicating the extent to which the spring has been wound, and in the above-noted '135 and '544 U.S. patents, the tension in the band brake is measured with a strain gauge producing an electrical output signal which is transmitted to a miroprocessor for computing the workout level. In the above-noted '890 U.S. patent, a weight is positioned between one end of the band brake and an anchoring spring. A pointer extends outwardly from the weight in the direction radially to the flywheel to terminate at an adjacent graduated scale. In the aforementioned '216 and '491 U.S. patents, the tension on the band brake is not measured directly, but rather is "ascertained" by the position of a hand lever used to apply the tensile load on the band brake.
Unfortunately, the foregoing energy measuring devices or ergometers are prone to inaccuracy due to the underlying assumption that the tension on the band brake is related to the work being expended by the rider in a repeatable, known relationship. However, the work being expended by the rider is in actuality related to the friction load between the band brake and the flywheel, which load is being overcome by the rider. For a given tension load on the band brake, this friction force varies with the coefficient of friction existing between the band brake and the flywheel. The coefficient of friction may be dependent upon numerous factors that change over time, for example, the extent of wear on the band brake, the atmospheric moisture and the cleanliness of the environment in which the cycle is located, etc. As a result, ergometers that measure the tensile load on the band brakes of stationary exercise cycles may not provide an accurate measurement of the force being overcome by the ride and, thus, the energy being expended by the rider.